This invention relates to a plasma addressed liquid crystal display panel with a thinned cover sheet.
U.S. Pat. No. 5,077,553 discloses apparatus for addressing data storage elements. A practical implementation of the apparatus shown in U.S. Pat. No. 5,077,553 is illustrated schematically in FIG. 2 of the accompanying drawings.
The display panel shown in FIG. 2 comprises, in sequence from below, a polarizer 2, a channel substrate 4, a cover sheet 6 (commonly known as a microsheet), a layer 10 of electro-optic material, an array of parallel transparent data drive electrodes (only one of which, designated 12, can be seen in the view shown in FIG. 2), an upper substrate 14 carrying the data drive electrodes, and an upper polarizer 16. The channel substrate 4 is typically made of glass and is formed with multiple parallel channels 20 in its upper main face. The channels 20 are filled with an ionizable gas, such as helium. A ground electrode and a strobe electrode (not shown) are provided in each of the channels 20. The channels 20 are orthogonal to the data drive electrodes and the region where a data drive electrode crosses a channel (when viewed perpendicularly to the panel) forms a discrete panel element 22. Each panel element can be considered to include elements of the layer 10 and the upper and lower polarizers 2 and 16. In the case of a color display panel, the panel elements include color filters (not shown) between the layer 10 and the upper substrate 14. The region of the upper surface of the display panel that bounds the panel element constitutes a single pixel 24 of the display panel.
As explained in U.S. Pat. No. 5,077,553, when a suitable potential difference is established between the strobe and ground electrodes in one of the channels, the gas in that channel forms a plasma that provides a conductive path at the lower surface of the cover sheet 6. If the data drive electrode is at ground potential, there is no significant electric field in the volume element of electro-optic material and the pixel is considered to be off, whereas if the data drive electrode is at a substantially different potential from ground, there is a substantial electric field in that volume element of electro-optic material and the pixel is considered to be on.
It is conventional to assemble a display panel of the kind shown in FIG. 2 by forming a channel substrate assembly, including the channel substrate and the cover sheet, forming an upper substrate assembly, including the upper substrate, the data drive electrodes, and the layer of electro-optic material, and attaching the upper substrate assembly to the channel substrate assembly. In manufacture of the channel substrate assembly, the cover sheet is placed over the upper surface of the channel substrate and is sealed to the channel substrate around the periphery thereof.
The operation of attaching the cover sheet to the channel substrate sometimes results in damage to the cover sheet, such that the cover sheet, and possibly the entire channel substrate assembly must be discarded as scrap. A common cause of damage is a particle, such as a shard of glass, being caught between the channel substrate and the cover sheet, such that the cover sheet is sheared when it is pressed against the channel substrate.